Watts’s ordeal came when she had been strapped into a chair while a wall of water flooded over her, making it hard to come up for air.

The 44-year-old revealed her near-death experience in the January edition of Easy Living magazine.

‘When we were shooting in the tank, we really weren’t acting,’ she said.

The actress added: ‘We were anchored in these chairs as the wave machine broke over us. There was a moment when I came up for air but couldn’t get out of the chair. I was already out of breath and the chair took me under again.’

She went on to describe The Impossible as her most challenging project to date, even more so than the film she is shooting at the moment – a biopic of Princess Diana.

The film is based on a true story of a family’s experiences in the Indian Ocean tsunami of 2004 and also stars Ewan McGregor.

At the UK premiere of The Impossible this week, Naomi told media about her ‘courageous and heroic’ character Maria Belon.At the BFI IMAX cinema in London, the J. Edgar star said: ‘Every mother wakes up with fear of her children’s safety, so I just cannot imagine how she dealt with it.

‘I consider myself one of those people who are just hopeless in a crisis, but she said she never felt more connected to her centre and every decision she made felt like the correct one.’You kind of crave to have that. But it’s hard.’